Post a series whose premise as well as plotline involves parallel universes and/or alternate dimensions

Fairy Tail

"Edolas" is an alternate universe counterpart of the Fairy Tail Guild from Earth Land. in Edolas all The members are the same as the Earth Land Fairy Tail Guild, except for Erza Scarlet's Edolas counterpart, Erza Knightwalker, who is instead part of the Edolas Royal Army and is known as the Fairy Hunter. At least half of the Edolas Fairy Tail members were killed door Knightwalker during her Fairy hunts.Another big difference between the two guilds is that nearly all of the members of the Edolas Fairy Tail Guild have different personalities and appearances than their Earth Land counterparts. like this Edolas Natsu every one have their counter parts with different personalities.......... ehe he he

Edolas Natsu Eartling Natsu

Tengen Toppa Gurren Lagann

Dragon Ball has parallel univers, Pandora Hearts have also parallel dimension, of alternate dimension, I don't remember the difference! D: But you've understood... I hope XD

Amnesia- there are several parallel universes in it

Steins; Gate

Project A-Ko: Uncivil Wars takes place in a different universe than the main Project A-Ko series (though I don't think the universes are actually connected). the goal of the bad guy in this toon is to basically eliminate all universes and create a single one in their place.

Mahou Shoujo Madoka Magica sort of does.